Fig. 8.

Competition of unlabeled ligands against binding of ¹²⁵I-α-BTX. Panel A- Intact cells expressing α4 quintuple mutant and β2 subunits were incubated with ¹²⁵I-α-BTX (10-30 nM) for 15 minutes in the presence of specified concentrations of the following competing ligands: ACh (filled circles), nicotine (open circles), epibatidine (open squares), dihydro-β-erythrodine (open triangles). Panel B- Intact cells expressing the α4 quintuple mutant (filled circles), the α3 quadruple mutant (open circles), or the α2 quadruple mutant (triangles), each with the β4 subunit, were incubated with ¹²⁵I-α-BTX for 15 minutes in the presence of the indicated concentrations of nicotine. Smooth curves are fits of the Hill equation to the data, with the fitted parameters given in Table 3.